1. Field
One or more embodiments of the present invention relate to an image photographing apparatus, method and medium, and more particularly, to an image photographing apparatus, method and medium that can enhance color reproducibility and sensitivity.
2. Description of the Related Art
Devices with built-in cameras, such as digital cameras and camera phones, are currently in widespread use.
Generally, a camera includes a lens and an image sensor. The lens collects light reflected from a subject, and the image sensor detects the light collected by the lens and converts the detected light into an electrical image signal. Image sensors are largely classified into camera tubes and solid-state image sensors. Major examples of solid-state image sensors include charge coupled devices (CCDs) and complementary metal oxide silicons (CMOSes).
In order to increase resolution of an image acquired by such a camera, a conventional technique of reducing a unit area of each pixel in a sensing region, while maintaining a total area of the sensing region has been used. In other words, if the unit area of each pixel is reduced, the number of pixels will be increased by the reduced unit area, resulting in a high-resolution image. However, while a high-resolution image can be obtained using the conventional technique, it is difficult to obtain a high-sensitivity image. This is because the amount of light reaching each pixel is reduced by the reduced unit area.
Japanese Patent Publication No. 2004-304706 describes a solid-state photographing apparatus, which arranges white filters in all directions from a green filter among green, blue, red and white filter segments, and a signal processing method used by the solid-state photographing apparatus. This conventional art relates to a technology for guaranteeing an amount of signal charge and resolution, and enhancing color reproducibility even when pixels are miniaturized. However, it fails to suggest a method for preventing a reduction in sensitivity due to the miniaturization of pixels.
In addition, U.S. Pat. No. 5,965,875 discloses a stack-type image sensor, which can extract all of red (R), green (G) and blue (B) signals from a pixel. This conventional art uses the differences in absorption depths in a silicon layer of light of different wavelengths, and detects the R, G and B signals at different depths in the silicon layer. In this case, since all of the R, G and B signals can be obtained from a pixel, resolution of an image can be enhanced. However, it is not easy to precisely separate the R, G and B signals from the silicon layer. Hence, color reproducibility deteriorates, which, in turn, makes it difficult to obtain a high-quality image.
Korean Patent Publication No. 2005-0098958 seeks to complement characteristics for G by placing a G component in a neighboring pixel. However, since the G component may still be included between R and B components in an extracted signal, color crosstalk occurs. To solve this problem, “Image Recovery for a Direct Color Imaging Approach Using a Color Filter Array” was published in the Electronic Imaging Conference held in January 2006. This conventional art is a research result of professor Takahiro Saito from Kanagawa University. In this conventional art, magenta-green filters in, for example, a Bayer pattern is simultaneously used in the stack-type image sensor disclosed in U.S. Pat. No. 5,965,875. Therefore, the deterioration of color characteristics due to crosstalk caused by photons can be compensated for by extracting narrow band B and R using the magenta filter. At the same time, G can be obtained using the G filter while B and R bands are blocked. However, a sensitivity loss of this technology is significant since its light reception sensitivity to G is reduced to ⅓ of its original sensitivity.